Comprehensive Treatment Strategy for Banana Inflorescence Bract to Synthesize Biodiesel and Bioethanol Through Fungal Biorefinery

Abstract

Banana inflorescence bract (BIB), an agro-waste is sporadically explored for second-generation biofuel production in spite of having considerable holocellulosic composition (cellulose-35.56%, w/w; hemicellulose-22.41%, w/w). In this study, an attempt has been made to utilize this substrate for fermentable sugars (pentose-C5 and hexose-C6) extraction which were employed for the co-production of microbial lipids and ethanol using Rhodosporidium toruloides NCIM 3547 and Saccharomyces cerevisiae respectively. Since, a considerable amount of lignin (8.78%, w/w) is present in BIB, a hybrid pretreatment and carbohydrate hydrolysis through microwave (160 W) assisted mild H2SO4 acid 2.5% (v/v) was adopted. The resultant liquor contains holocellulosic sugars (C5 and C6 sugars), out of which xylose (10.40 ± 0.49 g/L) and glucose (51.48 ± 1.14 g/L). Hence, it was used as the growth medium for R. toruloides to produce lipids i.e., single cell oil (SCO). The maximum lipid content was found to be 44.89 ± 1.25 (%, w/w) containing total saturated fatty acids of 89.07% which justifies its potential application in biodiesel production. On the other hand, the pretreated solid fraction containing cellulose was saccharified using cellulolytic enzyme produced by Aspergillus sp. with saccharification (%) of 69.99 ± 0.30 (%, v/w) and yield of 27.22 ± 0.33 g/L of reducing sugar. This enzymatic hydrolysate was used for ethanol production by Saccharomyces cerevisiae resulting in an ethanol yield of 12.70 ± 0.09 g/L and productivity of 0.132 g/L/h. Based on this outcome, a sustainable route for agro-waste management of BIB was laid by favouring the integrated production of biodiesel and bioethanol towards a biorefinery approach. Exploration and utilization of an agro-waste, banana inflorescence bract is established as a potent feedstock for the co-production of single cell oil and bioethanol is reported for the first time. Microwave-assisted mild acid pretreatment was performed for effective delignification and hydrolysis of holocellulosic components. The resultant liquid hydrolysate consisting of lignin degradatory compounds, pentose (xylose) and hexose (glucose) sugars was used as a growth medium for producing single cell oil, proving its potential application in biodiesel production. Further, the pretreated solid cellulosic fraction was saccharified using crude cellulolytic enzymes and an enzymatic hydrolysate was used for the production of bioethanol through two different fermentative strategies. This study reveals that banana inflorescence bract could act as suitable biomass towards the biorefinery approach. Its complete utilization paved the way for agro-waste management that is not in existence so far according to the authors’ knowledge